"ERROR -- Invalid Value"

[spice freak]

Hi,

I am trying to do AC Sweep Analysis. Every time PSPICE gives me this error:

"ERROR -- Invalid Value"

What could be the reason?

Thanks.

[spice freak]

Hi,

OK, I got it solved.

Now, the problem is I need some experimental starting values for my capacitors for the COMMON SOURCE amp.

Thanks.

[lineup]

C vs R-load gives the lower rolloff freq (-3dB)

For such I use: uF x kOhm
The higher this value ( C x RL ), the lower Rolloff Frequency

My target value is at least 47 uFkOhm. This gives -3dB at 3.38 Hz
For 100 kOhm load, I this means 0.47uF (470nF).

Formula:
-3dB frequency = 1/[ 2pi x C x R ] ... where 2pi = 6.28

uFkOhm value = Frequency -3dB
10 = 15.9 Hz
22 = 7.23 Hz
47 = 3.38 Hz
100 = 1.59 Hz (if you would use 1uF for 100 kOhm load.

[lineup]

To match C2 = 470 nF (47 uFkOhm)
you will need make input cap C1 so
that you get a value >= 47 uFkOhm
Otherwise input rolloff will be limit of lower freq rolloff

C1 sees: R1 // R2 (6k2 and 4k7)
The combined load (=the input impedance) is:
1 [ (1/R1) + (1/R2) ] ... which give 2673 Ohm = 2k67

47/2.67 = 17.6 uF ... to give 47 uFkOhm
So, C1 needs to be 18 uF or more, to match the output RC value

[spice freak]

Thanks!

it makes a lot more sense now.

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